Method of chill casting brass and other copper alloys containing zinc



Patented Apr. 8, 1952 METHOD OF CHILL CASTING BRASS AND OTHER COPPER ALLOYS CONTAINING ZINC Neil Douglas Gordon Robertson, Hartsbourne, Bushey Heath, and George William Browse, London, England, assignors to The Non-Ferrous Die Casting Company Limited, London,

England No Drawing. Application July 23, 1949, Serial No. 106,498

6 Claims.

This invention relates to the casting of brass and other copper alloys containing zinc in metal moulds or dies, i. e. by the so-called permanent die casting, and is particularly applicable to gravity casting, though it can also successfully be used in low pressure casting.

As hitherto practiced the casting of zinc-containin alloys in permanent dies is subject to the great disadvantage that zinc oxide builds up on the die faces in a very firmly adherent form, and after every few castings the die must be scraped and chipped to remove the deposit. This is wasteful of time and labor, and the continual scraping of the die faces soon renders the die unfit for accurate casting owing to dimensional changes.

Our researches have shown that the firm attachment of the build-up of zinc oxide to the die faces is due to the presence in the build-up of particles of metallic zinc which appear to anchor the oxide deposit to the die face.

It is an object of this invention to provide means whereby this build-up is avoided wholly or in part and the deposit is prevented from firmly adhering to the die face. A further object is to provide a dressing which, when applied to the die face before casting, prevents or diminishes the build-up of zinc oxide on the die face. A still further object is to provide an improved method of casting of brass and other copper-zinc alloys in permanent dies.

These objects are achieved by the invention now to be described.

According to the present invention there is applied to the runners, die-faces or cores used in the chill casting of brass or other copper alloy containing zinc, a dressing of a metal oxide capable at pouring temperatures of reduction to a lower oxide by metallic zinc. Examples of such metal oxdies are manganese dioxide, manganese sesquioxide, trimanganese tetroxide, ferric oxide, triferritetroxide. These may be used singly or in admixture amongst themselves or with inert diluents. Manganese dioxide is found to give the most consistently successful results, and in the following more detailed description the invention will be described with reference to manganese dioxide. It is to be understood that in place of manganese dioxide we may use any of the oxides named or any other metal oxide reducible to a lowe roxide by metallic zinc at pouring temperatures.

The manganese dioxide dressing may be applied in the form of an aqueous suspension by spraying 2 or dipping. In order to maintain the oxide in suspension the mixture of manganese dioxid and water may be mechanically stirred. Dispersing agents, such as sulphite cellulose pitch, sulphated long-chain fatty alcohols, or alkylnaphthalenesulphonates, may be added.

Manganese dioxide acts as an insulator and so helps to maintain the fluidity of the molten metal in the die. If desired one of the usual lubricants, e. g. powdered graphite, may be added to the suspension.

A suitable dressing may be made by stirring one part of powdered manganese dioxide into ten parts by weight of water to which has been added 0.25 to 0.30 part by weight of a 10% solution of tannic acid in commercial alcohol. The mixture is preferably sprayed on to the die. After the first casting, the die will of course be hot, and we find it advantageous to cool it down to about 200-250 C., usually by dipping in water. At such temperatures, or even below 200 C., an effective dressing of manganese dioxide is produced on the die.

Preferably, before applying the dressing we remove any particles of metal left on the die from a previous casting by the use of a pressure spray.

When brass or other copper-zinc alloy is cast in a die treated with a dressing of manganese dioxide according to the invention a perfectly clean casting results, and even after a number of successive castings there is little or no build-up of zinc oxide on the die. Any deposit on the die is readily removed in the cooling dip or by the light brushing which precedes the application of the dressing for the next casting.

The dressing has been found successful even in such difficult cases as lead brasses containing up to 2-3% of lead, which with ordinary dressings show a heavy build-up after only a few castings.

What is claimed is:

1. The method of chill casting brass and other copper alloys containing zinc in metal molds or dies, which includes the step of applying to the die faces a dressing of a metal oxide capable of being reduced to a lower oxide by metallic zinc at pouring temperatures.

2. The method of chill casting brass and other copper alloys containing'zinc in metal molds or dies, which includes the step of applying to the die faces a dressing consisting essentially of a substance selected from the group consising of the higher oxides of iron and manganese.

3. The method of chill casting brass and other copper alloys containing zinc in metal molds or 3 dies, which includes the step of applying to the die faces a dressing of manganese dioxide.

4. The method of chill casting brass and other copper alloys containing zinc in metal molds or dies, which includes the step of applying to the die faces a dressing of manganese dioxide in the form of an aqueous suspension.

5. The method of chill casting brass and other copper alloys containing zinc in metal mold-s or dies, which includes the step of applying to the die faces a dressin of manganese dioxide in the form of an aqueous suspension, the die faces having previously been cleaned from adhering particles of metal by means of a high-pressure spray.

6. The method of chili casting brass and other copper alloys containing zinc in metal molds or dies, which includes the steps of first cooling the die to a temperature within, the range ZOO-250 C. and then applying to the die faces a dressing of manganese dioxide in aqueous suspension.

NEIL DOUGLAS GORDON ROBERTSON. GEORGE WILLIAM BROWSE.

4 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 49,272 Hursh Aug. 8, 1865 93,155 Johnston July 27, 1869 119,682 Yielding Oct. 3, 1871 335,628 Riddle Feb. 9, 1886 413,815 Taylor Oct. 29, 1889 843,426 Acheson Feb. 5, 1907 1,505,176 Udale Aug. 19, 1924 1,517,778 Frohman Dec. 2, 1924 1,560,838 Meloche Nov. 10, 1925 1,770,684 De Witt July 15, 1930 1,837,772 Hailwood Dec. 22, 1931 1,934,626 Nagelvoort Nov. 7, 1933 1,965,340 Heinicke July 3, 1934 1,995,349 Heinicke Mar. 26, 1935 2,259,457 Croll Oct. 21, 1941 OTHER REFERENCES Die Casting by Herb, 1936, page 249. 

1. THE METHOD OF CHILL CASTING BRASS AND OTHER COPPER ALLOYS CONTAINING ZINC IN METAL MOLDS OR DIES, WHICH INCLUDES THE STEP OF APPLYING TO THE DIE FACES A DRESSING OF A METAL OXIDE CAPABLE OF BEING REDUCED TO A LOWER OXIDE BY METALLIC ZINC AT POURING TEMPERATURES. 